A multicentre, double-blind, between-patient study was carried out to evaluate the efficacy and tolerability of oxiracetam (800-mg tablets), in comparison with placebo, each given twice daily for 12 weeks to patients suffering from primary degenerative, multi-infarct or mixed forms of dementia. Efficacy was assessed by the Inventory of Psychic and Somatic Complaints in the Elderly (IPSC-E), administered at entry and after 4, 8 and 12 weeks of treatment, and by the Blessed Dementia Scale and the Newcastle Memory, Information and Concentration Scale (NMICS), administered at the beginning and at the end of the study. Three hundred and seven patients were enrolled, 18 of whom were excluded from the analysis because of violation of the protocol. Two hundred and eighty-nine patients were analyzed (145 m, 144 f, mean age 73 years) and 272 completed the study; 3 patients in each treatment group were withdrawn because of poor tolerability, 10 because of poor compliance and 1 patient because of the occurrence of a cerebral stroke. A significantly (p < 0.01) different effect, in favor of oxiracetam, was observed in the three main efficacy criteria (i.e. IPSC-E, Blessed Dementia Scale and NMIC total scores), and confirmed by descriptive analyses carried out on some subitems of the scales used. Thirty-one patients on oxiracetam and 27 on placebo complained of a total of 35 and 32 minor unwanted effects, respectively. No clinically or statistically significant changes were observed on routine laboratory examinations.